Recently, high-energy infrared lasers have been developed for a number of applications. Typically, CO.sub.2 (10.6.mu.m wavelength) lasers operating at irradiance levels to about one Kw/cm.sup.2 and higher have been used in manufacturing plants as welding and drilling tools, for scoring semiconductor sheets, etc. Many high-power lasers are used in laboratories, both as investigatory tools and in research on laser systems. Devices using powerful lasers have also been developed for communications, range finding and other military and civilian purposes. Other high-energy infrared lasers using deuterium and hydrogen halidies are being developed.
The energy transmitted by these lasers can be very dangerous to personnel working with the lasers or others who accidentally intercept the beam. These beams can be very damaging to the eyes of such persons and, in the higher power ranges, can cause severe burns and other physical damage.
Simply interposing a filter which absorbs or diverts the laser beam has been found to be insufficient. The localized energy application is so great and so rapidly applied that the filter material is often immediately melted and/or vaporized. Even highly efficient reflectors may be destroyed when surface dirt or dust absorbs sufficient energy to cause localized overheating and destruction of the reflector, destroying its protective capacity.
Attempts to protect personnel against such laser beams without extreme measures have generally not been successful. One proposed system, as described in U.S. Pat. No. 3,578,842, utilizes an exploding mirror in an optical system which might be impinged by a laser system. The laser energy causes an explosive on the mirror to detonate, thereby protecting the operator while destroying the optical system. Preferably, of course, he should be protected while allowing his equipment to continue to function. Also, this does not protect a worker who is directly in the path of the laser beam. Laser radiation is especially damaging to the eyes of such workers.
Continued operation of the laser system is especially important in applications such as laser rangefinders, where the high-energy laser beam must pass through a protective rangefinder window. Dust or dirt on this window may absorb sufficient energy to cause localized overheating and destruction of the window. As in the case of personnel protective device, this window should be capable of protecting the rangefinder laser (here, against environmental damage, such as from rain or wind-blown dust) while permitting continued effective laser operation.
Protective devices using reflectors to reflect away incident infrared laser beams must be highly reflective in the infrared region, while permitting transmission of visible light. Unless a very high percentage of the incident infrared radiation is reflected, the portion absorbed by the protective device may be sufficient to cause localized overheating, thermal shock and permanent damage to the protective device.
Thus, there is a continued need for effective protective windows to protect personnel and equipment from damage from high-energy lasers while permitting continued operation of the overall system, at least temporarily.
It is, therefore, an object of this invention to provice a protective window for use with high-energy infrared lasers which overcomes the above-noted problems.
Another object of this invention is to provide an eye protection means for personnel subjected to high-energy laser radiation.
Still another object of this invention is to provide a self-cleaning window for use with high-energy lasers.
A further object of this invention is to improve the reflectance of high-reflectance protective surfaces.
Yet another object of this invention is to provide a means for protecting radiation sensors from high-energy infrared radiation.